(1) Field of the Invention
The present invention relates to a motor-driven disk brake system for generating a braking force by utilizing a motor torque, and a control device for the motor-driven disk brake system.
(2) Description of Related Art
There is a motor-driven disk brake system that comprises: a pressing member (piston) for pressing a brake pad against a disk rotor; and an electric caliper including a motor and a rotary-to-linear motion converter for converting rotation of the motor to a linear motion to transmit the linear motion to the pressing member, such that the pressing member is moved forward according to rotation of a rotor of the motor so as to press the brake pad against the disk rotor, thereby generating a braking force. Normally, the motor-driven disk brake system uses a sensor to detect a stepping force or a stroke applied by a driver to a brake pedal and to control rotation (rotational angle) of the electric motor, based on a detected value, and thereby obtains a desired brake force (pressing force).
Japanese Patent Public Disclosure No. 2003-113877 discloses an example of a motor-driven disk brake system of the above-described type, which has a fail open mechanism in an electric caliper, so as to move back a pressing member when a power supply from a control device to a motor is stopped.
However, the motor-driven disk brake system disclosed in Japanese Patent Public Disclosure No. 2003-113877 often encounters a problem: When the pressing member is moved back upon stop of power supply to the motor as described above, the backward movement of the pressing member is accelerated due to inertia, so as to move the pressing member back beyond a predetermined position. Therefore, when the system is activated next time, it takes a certain amount of time to move the pressing member to a standby position of non-braking state.